Evaluation of position tracking technologies for user localization in indoor construction environments Hiam M. Khoury 1 , Vineet R. Kamat ⁎ Department of Civil and Environmental Engineering, University of Michigan, 2350 Hayward St., Room 2340 G.G. Brown Building, Ann Arbor, MI 48109-2125, USA abstract article info Article history: Accepted 27 October 2008 Keywords: Construction GPS Indoor GPS Tracking UWB WLAN Evolving technologies such as location-aware computing offer significant potential of improving important decision-making tasks on construction sites by providing support for tedious and time-consuming tasks associated with timely and accurate access to project information. For example, rapid and convenient access to contextual project information, through continuous position tracking of engineers, managers, and inspectors, can lead to significant cost and time savings due to the accuracy and immediacy with which relevant project information can be made available to field personnel. Considering the spatial expanse and dynamic nature of typical construction projects, mobile users need to be constantly tracked both outdoors as well as indoors. The Global Positioning System (GPS) is an attractive option for outdoor environments, but is not suitable for indoor applications because it needs a clear line-of-sight to orbital satellites in order to track position. As a result, alternate means of tracking users' location in indoor environments without relying on GPS is needed. This paper presents research that investigated the effectiveness of three wireless technologies for dynamic indoor user position tracking. In particular, Wireless Local Area Networks (WLAN), Ultra-Wide Band (UWB), and Indoor GPS positioning systems are evaluated and compared. Experimental results demonstrate the ability of Indoor GPS, in particular, to estimate a mobile user's location with relatively low uncertainty (1 to 2 cm). © 2008 Elsevier B.V. All rights reserved. 1. Introduction In recent years, the need for indoor localization has been rapidly expanding in many fields [16] and currently offers significant potential on construction sites in particular [30]. Field construction tasks such as inspection, progress monitoring and others require access to a wealth of project information. Currently, site engineers, inspectors and other site personnel, while working on construction sites, have to spend a lot of time in manually searching into piles of papers, documents, and drawings to access the information needed for supporting the tasks at hand. Location-aware computing offers significant potential of improv- ing such manual processes and supporting important decision- making tasks in the field. For example, instead of having to browse through detailed drawings and other paper based media, contextual project information can be automatically retrieved and visualized by continuously and accurately tracking mobile users' three-dimensional spatial context (i.e. position and orientation) [13]. The concept of context-aware information delivery [3] encom- passes the creation of a user centered mobile dynamic indoor and outdoor work environment, which has the ability to deliver relevant information to on-site mobile users by intelligent interpretation of their spatial characteristics so that they can take more informed decisions [25]. Global Positioning System (GPS), being a satellite- based navigation system, works very well outdoors but lacks support indoors and in congested areas. In addition, unlike outdoor areas, the indoor environment imposes different challenges on location discovery due to the dense multipath effect and building material dependent propagation effect [14]. There are many potential technologies and techniques that have been suggested to offer the same functionality as a GPS indoors, such as Wireless Local Area Networks (WLAN), Ultra-Wide Band (UWB) and Indoor GPS. By tagging users with appropriate receivers/tags and deploying a number of nodes (access points, receivers, transmitters, etc.) at fixed positions indoors, the location of tagged users can conceptually be determined and continuously tracked. The objectives of the paper are to describe three key wireless technologies applicable for indoor positioning, portray and compare the technical characteristics of these technologies through several conducted experiments, and highlight the extent to which each technology can be used to accurately calculate the positional context of a user in congested harsh environments such as those found on Automation in Construction 18 (2009) 444–457 ⁎ Corresponding author. Tel.: +1 734 764 4325; fax: +1 734 764 4292. E-mail addresses: hkhoury@umich.edu (H.M. Khoury), vkamat@umich.edu (V.R. Kamat). 1 Tel.: +1 734 764 4325; fax: +1 734 764 4292. 0926-5805/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.autcon.2008.10.011 Contents lists available at ScienceDirect Automation in Construction journal homepage: www.elsevier.com/locate/autcon